A series of progress in two-dimensional materials research of USTC

Recently, Cui Ping, Ph.D., International Center for Quantum Design of functional materials, National Laboratory of microscale materials science, Hefei, University of science and technology of China, worked with colleagues at home and abroad to reveal the universal atomic scale mechanism of edge reconstruction of serrated nanoribbons of transition metal disulfide compounds Furthermore, based on the adjustability of the found edge reconstruction model, it was realized for the first time in combination with the experiment The controllable growth of molybdenum selenide nanoribbons from the bottom to the top has been revealed Relevant achievements have been published in nano express [nano lett 17, 1097 (2017)] and nature commun 8, 15135 (2017)] (a) Schematic diagram of edge reconstruction of MOX 2 and (b) Wx 2 serrated nanoribbons In the middle illustration, the Mo edge is taken as an example to show the universal (2 × 1) reconstruction self passivation process As an important branch of two-dimensional material family, transition metal disulfide compounds (TMD) have great application prospects in the field of electronics, optics, spin electronics and other devices due to their adjustable intrinsic band gap, high carrier mobility, strong interaction with light field, strong intrinsic spin orbit coupling and valley degree of freedom When two-dimensional materials are integrated into devices, they will inevitably face various boundaries of the system, and their structural properties have an extremely important impact on the overall stability and performance of devices In view of this basic problem, Cui Ping and Li Zhenyu, and other internal and external collaborators, using the first principle calculation, systematically studied the structure, electronic properties and magnetism of MX2 (M = Mo, W; X = s, Se) serrated nanoribbons Structurally, this study reveals for the first time that there is a novel and universal (2 × 1) reconstruction mode of M-edge, that is, self passivation of edge metal atoms is realized by exchanging the positions of edge m and X atoms, resulting in a significant reduction of system energy (as shown in Figure 1) In terms of physical properties, taking MOX 2 zigzag nanoribbons as an example, it is shown that the reconstructed edge has robust edge metal state and unique spin order This study not only provides a possible new explanation for the origin of the edge metal states observed in the early experiments, but also provides an indispensable theoretical basis for the growth of band structure in the subsequent experiments It has important application value in the fields of Nano Electronics, spin electronics, optics and catalysis The work was published in nano lett 17, 1097 (2017) (a) Atomic force microscope (AFM) images of MoSe2 morphology at different growth temperatures; (b) first principle calculation and comparison of the structure and energy of different MoSe2 nanoribbons: the serrated edge energy reconstructed in the above figure is significantly lower than that of the armchair edge energy; the energy of the two in the following figure is similar Another challenge for the integration of two-dimensional materials into devices is to further reduce the dimensions of the system, such as the preparation of quantum dots, quantum wires, nanoribbons and so on With the decrease of two-dimensional material dimension, rich and peculiar physical properties will be derived However, the previous study of TMD nanoribbons is limited to top-down preparation by electron beam irradiation of transmission electron microscope (TEM) There are inevitably many defects on its edge, which greatly restricts the corresponding physical properties and device application Recently, Cui Ping and his colleagues, together with Professor Shi Zhigang of the University of Texas Austin and Professor Jin Chuanhong of Zhejiang University, worked together on the experimental research Based on the previous theoretical work on the edge reconstruction of TMD, they realized the controllable preparation of mose 2 nanoribbons for the first time in the world by the bottom-up method (as shown in Figure 2) Firstly, it is predicted theoretically that the growing islands will change from fractal structure to compact structure with the increase of growth temperature, which is verified by experiments However, when the growth temperature continues to rise, it is observed that the dense structure will further change into a quasi one-dimensional band structure, and its length and width can change with the growth conditions Based on this strange phenomenon, it is theoretically further speculated that the self passivation and reconstruction will occur on the serrated edge of MoSe 2, and the growth rate and further the growth rate of MoSe 2 can be determined by the energy and stability of different MoSe 2 edges Therefore, by adjusting the temperature and the ratio of Se: Mo, the concentration of Se on the substrate and the mode of edge reconstruction can be changed, so as to realize the controllable preparation of nanoribbons This conjecture is verified by the following comparative experiments and the first principle calculation Because of the universality of the self passivation reconstruction mode of the serrated metal edge of the TMD material, the growth mechanism controlling the morphology of the system through the edge reconstruction will also be applicable to other TMD systems This work was published in nature commun 8, 15135 (2017) Attached paper link: nano lett., 2017, 17 (2), PP 1097 – 1101 doi: 10.1021/acs.nanolet.6b04638 nature communications 8, article number: 15135 (2017) doi: 10.1038/ncomms15135